Page 48 - Build 151

Internal moisture
Combating internal moisture
Newer homes may be less draughty but concern is growing that they are accumulating too much internal moisture. Ventilation is key, and BRANZ is researching how to keep homes aired, warm and healthy.
BY STEPHEN MCNEIL, BRANZ BUILDING PHYSICIST
Mould growth in poorly ventilated home.
THE MOST PRESSING contaminant in New Zealand homes is internal moisture. It is produced constantly from many di erent sources and can be a challenge to manage e ectively.
Moisture damages health and home
Moisture absorbs readily into a wide range of materials and can take considerable time to remove from a home. The most e ective technique for managing moisture
is ventilation at its source, supplemented with a whole-of-house ventilation strategy. Moisture in the home can cause a variety
of problems including:
● health issues
● buildingmaterialdecay
● mould and fungi growth on surfaces. Internal moisture can also in uence inter- stitial condensation, and BRANZ’s vapour control in walls project is providing guid- ance on this.
Steps to managing indoor moisture
BRANZ Building Basics Internal moisture outlines several practical steps to help manage indoor moisture problems:
● Limit sources of moisture – where
this can’t be done, ensure moisture is
extracted where it is produced.
● E ectiveheating–warmerairhasahigher moisture-carrying capacity. Heating the indoor air lowers the relative humidity and encourages evaporation of moisture from surfaces. This means ventilation will remove more moisture from the building.
● Regular opening of windows.
● Installing an appropriate ventilation
system.
Take care venting dryers
Clothes dryers can emit 5 kg of water per load into the indoor air, so their proper venting outdoors is a good example of extraction of moisture at the source.
46 — December 2015/January 2016 — Build 151
FEATURE SECTION